Project Summary There currently is no licensed vaccine against Chlamydia trachomatis, the leading cause of bacterial sexually transmitted disease worldwide. Untreated genital chlamydial infection cause serious sequelae such as pelvic inflammatory disease, ectopic pregnancy, and infertility. A Chlamydia-secreted protein, designated as CPAF (chlamydial protease/proteasome-like activity factor), is responsible for degradation of the host MHC transcription factors RFX5 and USF1. Inhibiting CPAF activity will therefore be a feasible vaccination strategy for blocking chlamydial evasion of immune recognition. We have now provided direct evidence to demonstrate the effectiveness of such an approach using recombinant (r)CPAF and IL-12 in an intranasal (i.n.) delivery system. Intranasal vaccination with rCPAF and IL-12 induced robust antigen-specific IFN- production, significantly reduced bacterial shedding upon intravaginal (i.vag.) chlamydial challenge and significantly accelerated the resolution of infection compared to mock-immunized (PBS) mice. Importantly, rCPAF+IL-12 vaccinated mice exhibited protection against pathological consequences of chlamydial infection, including mesosalpingeal inflammation and development of hydrosalpinx and oviduct dilation. The rCPAF+IL-12-mediated resolution of chlamydial infection and protection against inflammatory pathology was highly dependent on endogenous IFN- production and the action of antigen-specific CD4+ T cells. Based on our notable body of evidence, we hypothesize that CPAF vaccination promotes preservation of fertility and reduces inflammatory pathology after genital Chlamydia infection by enhancing bacterial clearance within the upper genital tract via antigen-specific IFN- secreting CD4+ T-cells with the participation of local phagocytic cells. We will test this hypothesis by; (1) Examining the direct effect of i.n. CPAF vaccination on the preservation of fertility after genital chlamydial challenge; (2) Determine the relationship between the reduction in chlamydial organisms and the infiltration of antigen-specific CD4+ T cells within the upper genital tract induced by CPAF vaccination; (3) Investigating the mechanism(s) by which IFN- producing CPAF specific CD4+ T cells enhance bacterial clearance and prevent the development of urogenital pathology associated with chlamydial infection.